Prostate cancer, diagnosed in over 200,000 American men each year, remains a significant cause of mortality; in 2007, it will be responsible for approximately 27,000 deaths. Advances in screening have fostered tremendous improvements in detection, such that most prostate cancers are now diagnosed at extremely early stages amenable to cure by surgery or radiation. Nonetheless, although cure for these early cancers is readily possible, the therapy that produces this cure often significantly diminishes quality of life. A complication of prostate cancer control is that the prevalence of undiagnosed, apparently occult prostate cancer is high relative to the incidence of symptomatic or fatal disease. Prostatic cancer among many men is occult, non-symptomatic and not life-threatening; these men will die with, rather than of, their disease. Many screen-detected prostate cancers, especially those diagnosed at a very early stage, might otherwise never cause symptomatic disease. Given the substantial morbidity of prostate cancer therapy, it would be of great benefit to identify men with early stage disease for whom radical intervention can be delayed. The focus of this study is low grade, low-volume prostate cancer (LGLV prostate cancer). Prostate cancer in these men is increasingly being monitored by an approach known as expectant management (EM). The probability that an early-stage prostate cancer will develop into aggressive disease may be altered by environmental exposures, including diet. There is observational evidence that a diet high in fruits and vegetables is negatively associated with the risk of prostate cancer initiation and progression. It would be valuable to know whether adoption of a plant-intensive diet could decrease the risk that LGLV prostate cancer progresses to more advanced stages. This proposal is to assess whether a diet emphasizing plant consumption decreases the probability that LGLV prostate cancer in EM patients progresses to a more aggressive form of cancer that merits active treatment. The intervention will be conducted through one of the leading cooperative oncology research groups: Cancer and Leukemia Group B (CALGB). Patients will be enrolled through individual CALGB and Cooperative Community Oncology Program clinical sites. Experimental patients will receive a telephone-based intervention that has been shown to alter the dietary practice of prostate cancer patients; control patients will receive a packet of diet-recommendation materials issued by the NCI. Diet change will be evaluated by 24-hour recalls and by blood carotenoids. Disease will be monitored by PSA and appropriate clinical surveillance for 24 months. PUBLIC HEALTH RELEVANCE: Prostate Cancer is diagnosed in over 200,000 American men each year. A substantial proportion of prostate cancer is low-grade, low-volume and apparently indolent. Expectant management, which does not lessen the quality of life as intervention does, may be appropriate for such patients; interventions intended less to cure disease than to forestall its progression to a more aggressive phenotype are worth investigation. This proposal is to investigate whether a dietary intervention emphasizing a plant-based diet slows or blocks progression of prostate cancer.